Electronic devices, including organic electronic devices, continue to be used more extensively in everyday life. Examples of organic electronic devices include Organic Light-Emitting Diode (“OLED”) displays. Due to the sensitivity to moisture and oxygen of the organic materials (e.g., transport materials, emissive materials) and the cathode materials used in organic electronic devices, these devices typically have rigorous package requirements for practical applications. Two types of packaging structures adopted for organic electronic devices include (1) a sealing can with an air gap and solid-state desiccants and (2) a thick metal solder layer directly attached to a common cathode. The sealing may include glass and ceramic materials, metals and metal alloys, other materials that prevent significant diffusion of moisture or oxygen, and combinations thereof. As will be described below, either or both packaging structures may not provide sufficient heat dissipation.
The radiation emission efficiencies of OLED pixels are typically in a range of approximately one to twenty candelas per ampere (1-20 cd/A). For a full-color display with a fifty percent (50%) aperture ratio and with a circular polarizer with approximately forty percent (40%) optical transmission, the pixel current density is in a range of approximately thirty to six hundred milliamperes per square centimeters (30-600 mA/cm2) for an emission intensity of approximately 400 cd/m2. At an operation voltage of approximately five volts (5 V), the corresponding input electric power density is in a range of approximately 0.15-3.0 watts per square centimeter (W/cm2). Aside from the conversion into light energy for light emission, much of the input electrical energy is converted into heat. When thermal conduction from the emission layer to the surroundings is not sufficient, substantial panel heating will occur.
A conventional active matrix (“AM”) driven device includes a common cathode. This common electrode layer can be subjected to high current density when the display size is large or when the emission intensity increases above certain levels. In such cases, if the heat flowing from the radiation-emitting region to the ambient air is insufficient, a significant temperature rise will also take place in the device. In particular, the operation lifetime of OLED devices is dependent on operation temperatures. For example, devices with emissive layers using poly(phenylenevinylene) (PPV) derivatives with yellow or orange colors, the operation lifetime can be approximately 35 times shorter at 80° C. than at 25° C. Other electronic devices may experience reduced lifetimes due to higher operating temperature.
In a conventional OLED device, the common cathode can be covered by an epoxy layer and glass sheet. Another conventional OLED device can be covered by a metal cap that has a desiccant. The metal cap is attached using an adhesive. These OLED devices may have thermal resistance coefficients that are typically greater than 150° C. cm2/W . The corresponding temperature rise of the radiation-emitting electronic components could be higher than 10° C. when operating at 200 cd/m2 for a display having an area of approximately 3-6 cm2. Outdoor display applications and lighting panels can have emission intensities of 500-2000 cd/m2 and 2000-5000 cd/m2, respectively. AM-driven OLED displays in such applications may not be stably operated at such high brightness levels, and the device temperature may not even be stabilized due to insufficient heat flow out of the device (a phenomenon known as thermal run-off).
Heat dissipation issues are not unique to organic electronic devices. Inorganic (e.g., silicon-based) integrated circuits (“ICs”) can generate significant amounts of heat. Most notable are microprocessors (e.g., Intel Pentium™, AMD Athlon™, IBM PowerPC™ processors) due to their power requirements.